Ammonium perchlorate (AP) is the most commonly used high-oxygen carrier in propellants, explosives, pyrotechnics and ammunitions. Ammonium perchlorate is the major oxidizer used in composite solid rocket propellants carrying sufficient amounts of oxygen to oxidize not only the ammonium cation, but also substantial amounts of aluminum powder (about 15 weight %), binder (about 12 weight %), and curing agent (about 2 weight %). The performance of such composite solid rocket propellant formulations is measured in terms of their specific impulse (Isp) which for a typical ammonium perchlorate based propellant is about 265 sec. Besides providing a high Isp, the high-oxygen carrier in such composite propellant formulations must fulfill additional requirements. It must be hydrolytically stable to allow processing and storage of the propellant in the atmosphere, be compatible with the other ingredients used in the formulation, and must be relatively insensitive to impact, friction and heat.
Ammonium perchlorate is commercially produced on a very large scale electrochemically by anodic oxidation of chlorate. For example, the production of ammonium perchlorate at the Henderson Nev. facilities alone amounted to 76 million pounds per year in 1998. The major drawbacks of the use of ammonium perchlorate in propellant formulations are the generation of HCl as a combustion product giving rise to huge amounts of acidic rain, and its high toxicity to humans causing thyroid problems already at very low concentrations at the ppb level in drinking water. As a result, the large scale use of ammonium perchlorate in propellants is facing increasing scrutiny and likely congressional actions to restrict its use. Such actions have as yet not been taken due to the lack of a suitable high-performing green replacement. The problem of finding a suitable green replacement for ammonium perchlorate has been pursued for more than a century but so far has not been solved. Thus, there is an urgent need to find a green replacement for ammonium perchlorate in view of the global need for using high-performing solid propellant rockets for the launch of communication satellites, strategic missiles and space exploration missions.
Potential replacements for ammonium perchlorate should be environmental friendly (i.e., green), high-performing, thermally and hydrolytically stable. Such replacements are desirably highly energetic high-oxygen carriers. In general, the sensitivity of an energetic material increases sharply with its energy content. Therefore, finding highly energetic materials exhibiting low sensitivity is very difficult and rare. Similarly, high thermal stability generally requires very strong bonds which decrease the energy content, and it is difficult to find highly energetic materials which at the same time possess high thermal stability. Moreover, for large scale use, as in the solid propellant boosters for the major launch systems, it is imperative that the cost of the propellant ingredients is low, and simple high yield methods for their production can be devised. While some of these requirements had previously been incorporated into some energetic materials, the successful combination of all of these principles in a single compound presents an enormous challenge and has never been achieved before. For example, the synthesis of energetic ionic liquids derived from nitrato- or perchlorato-substituted borate, aluminate, phosphate or titanate salts has previously been disclosed by Christe and Drake in U.S. Pat. No. 7,771,549. However, the compounds of this patent are low-melting ionic liquids of insufficient oxygen balance, hydrolytical and thermal stability.
Accordingly, there is a need for a practical high-performing green replacement for ammonium perchlorate which can meet all the above requirements.